As a general rule CTO sheets are worth less than postally used and mint
unfranked.

Most (but not all) collectors consider postal use important, or at least
properly cancelled in the normal manner by the postal services. In other
words, if a sheet has been used in the mail, then that is best. Favour
cancelled, such as when I ask the postmaster to cancel some stamps that
I have bought, is next best (and for many high value stamps this may be
by far the majority of used stamps that are available), but most serious
collectors consider true CTO stamps (where the cancel has been applied
at the printers) as the lowest of the low. Many East German stamps are
almost worthless with printed cancels.